Device and Method for Reducing Loads

ABSTRACT

A device for reducing loads in a drive train of a wind turbine includes a machine support. The wind turbine includes a sensor means, a controllable damper means, an actuating means. The sensor means is configured to detect at least one variable characterizing vibrations and/or misalignments in the drive train. The controllable damper means is configured to produce at least one adjusting torque which compensates at least one torque associated with the load in the drive train. The actuating means is configured to actuate the damping means based on the at least one variable detected by the sensor means.

The present invention relates to a device and a method for reducing loads, in particular torsional vibrations as well as static and dynamic flexural torques, in the drivetrain of a wind turbine generator system.

1. Prior Art

Drivetrains, comprising components such as for example gear units, clutches and connecting elements (shafts), are important constituent parts of various electrical power generating systems, such as for example wind turbine generator systems, hydroelectric installations, etc.

The drivetrain performs the task of establishing a mechanical connection between a drive unit (for example a rotor of a wind turbine generator system) and a driven unit (for example a corresponding generator), via which power is transmitted through a rotational movement. Drivetrain components such as gear units serve the purpose of transforming the rotational speed and the torque at the drive unit to values that correspond to the operating range of the generator. Clutches are used as and when required for a disconnection between the drive unit and the driven unit and shafts establish the mechanical connection between the components involved. Further components, such as mechanical brakes or the like, may also be integrated in the drivetrain.

Since the components involved cannot be produced with any rigidity that may be desired, but have a finite rigidity, they may be induced to undergo natural vibrations. This may be caused, for example, by an non-constant input power (in the case of wind turbine generator systems for example due to wind surges or wind turbulences) or by outside disturbances. Vibrations of other origin may also increase the loads in the drivetrain, in the case of a wind turbine generator system for example tower vibrations or vibrations caused by the meshing engagements of a gear unit.

Further dynamic loads occur when the rotor blades pass the tower during their rotation. Depending on the number of blades, the reduction in wind speed immediately in front of the tower (in the case of upwind turbines) or in the wake of the tower (in the case of downwind turbines) results in periodic flexural torque loads in the drivetrain of the wind turbine generator system. Furthermore, static loads occur in the drivetrain if a misalignment between the components involved has occurred during the assembly of the shafts. This misalignment may also occur over time due to system components moving by themselves (e.g. creep in the case of elastomer mountings or settling in the case of screw connections) and consequently results in additional flexural torque loads and forces.

Vibrations and other additional loads have disadvantageous effects on the lifetime of the components involved, in particular of the gear unit. Constant pulsating loads and static additional loads increase the wear of the components concerned and lead to shorter replacement intervals, which represents a financial and technical burden on the operator of the system and the network and reduces the income from the system. In particular from the viewpoint of the presumably increasing proliferation of wind turbine generator systems in the offshore area in the foreseeable future, this aspect will play an ever-increasing role, since the replacement of damaged components of such systems is made even more difficult. There is therefore the aim of reducing these loads in order to increase the lifetime of the components.

DE 1 993 07 51 A1 discloses a method for reducing vibrations of components in a wind turbine generator system in which bearings of an elastomeric material that has a damping angle of at least 12° and a spring stiffness chosen such that the natural frequency of the vibrating components is less than 50 Hz are used in the system. A disadvantage of this is that respectively pre-known elastomeric materials must be used for the damping of specific vibrations and that adaptation to variable vibrations, for example to fluctuating vibrational amplitudes, is not possible.

Against this background, there is the need for improved solutions for reducing loads in the drivetrain of wind turbine generator systems, in particular torsional vibrations, as well as dynamic additional loads, that can be flexibly adapted to these loads that occur and ensure a better reduction. Static additional loads caused by misalignments are to be avoided, in order to provide further relief for the drivetrain as a whole.

2. Disclosure of the Invention

The present invention provides a device and a method for reducing loads, in particular torsional vibrations as well as static and dynamic additional loads, in the drivetrain of a wind turbine generator system, with the features of the independent patent claims. Advantageous refinements are the subject of the subclaims and of the description which follows.

3. Advantages of the Invention

The proposed measures allow a significant reduction of torque vibrations or torsional vibrations and loads in the drivetrain, in particular the gear unit, of wind turbine generator systems to be brought about. In particular in such wind turbine generator systems with a gear unit, a reduction of vibrations and loads is particularly advantageous on account of the exposed arrangement, the possible occurrence of wind surges, the periodically fluctuating loading of the rotor (reduction in wind speed immediately in front of the tower/in the wake of the tower when the tower is passed by rotor blade) as well as possible loads due to misalignment of one or more components.

The proposed measures make active damping of a mechanical vibration or loading possible in a drivetrain by activatable damping means. A torque or a force for vibration damping or load reduction is generated by the activatable damping means. The use of a suitable sensor system, in particular using acceleration sensors based on the Ferraris principle, but also for example force, rotational speed, rotational angle, position and/or torque sensors and a closed-loop and/or open-loop control technique made to match, allows particularly rapid, adaptive vibration damping and load reduction to be brought about. A suitable actuator system or adjustable, variable damping, as known per se, may be used for example here.

In order to damp torsional vibrations, the actuators advantageously bring about a rotation of the drivetrain or of the corresponding gear unit and/or lead to a prescribed damping sequence of a rotational movement. In this connection, even a slight rotational movement by a few degrees about the axis of rotation, in particular in conjunction with suitable speed-transforming transmissions, can bring about significant damping of torsional vibrations.

In addition, raising or lowering of the gear unit may be brought about by the actuator system. The moving or adjusting of at least one actuator or a combination of a number of actuators advantageously leads here to an equalizing of loads. The latter may be compensated both by periodic moving (in order for example to equalize loads from the reduction in wind speed immediately in front of the tower) and by the permanent adjustment (loads due to misalignment of system components). Also in the case of this approach to a solution, significant damping of additional loads can be brought about even by very small adjusting movements.

An activated active and/or retarded rotational movement of a drivetrain and/or of a gear unit housing integrated in a drivetrain is brought about by the present invention. In other words, damping of a rotational movement or of other loads is brought about by damping means, that is to say for example by corresponding actuators or springs, an adjusting torque resulting from a load torque or corresponding thereto being generated. The corresponding adjusting torque may be generated by controlled moving or adjusting of at least one damper or by a combination of the damping means described here. The damping movements can be set by suitable open-loop or closed-loop control means.

By choosing suitable closed-loop and/or open-loop control strategies, allowance can be made particularly advantageously for the particular requirements of wind turbine generator systems. For example, particularly advantageous damping can be brought about by correcting the effects of wake.

The damping devices proposed according to the invention with the associated closed-loop and/or open-loop control technique may be advantageously integrated in torque supports of the drivetrain, that is to say supports or fastenings for diverting a torque, preferably on a gear unit housing.

Therefore, a reduction of vibrations and loads in the drivetrain can be brought about by the measures according to the invention. This particularly allows a reduction of the loads in components of the drivetrain, in particular the gear unit, to be achieved. As a result, the mechanical loading of wind turbine generator systems is reduced, whereby the longevity of such systems is improved significantly. Furthermore, a reduction of vibrations also has the effect in particular of improving the output power of a generator of the wind turbine generator system, since otherwise variances in speed would have to be corrected in the generator.

As mentioned, the vibrations may be detected here by way of measuring acceleration on the drivetrain, preferably at different positions of the drivetrain, and/or by speed sensors. In the case of speed sensors, it may be advisable to derive the speed for determining the acceleration. The misalignment can likewise be detected at the points concerned by corresponding position sensors. Parallel models (as disclosed for example in EP 0 473 914 B1) and/or control engineering observers (with variables that occur, in particular torque, being calculated from the sensor variables with the aid of models) may be used with particular advantage. A path adaptation, which takes particularities and deviations from the theoretical model into consideration, may also be advantageously provided as part of the closed-loop control. Digital and/or analog transmission of an output sensor signal may be used for the closed-loop control, visualization, open-loop control and/or switching.

Significant drivetrain vibrations are induced in particular during emergency shutdowns (disconnection from the network or load shedding) due to the suddenly absent generator torque in wind turbine generator systems. Therefore, the device according to the invention can be used with particular advantage as part of an emergency shutdown procedure, in order thereby to significantly reduce vibrations that occur.

A closed-loop and/or open-loop control device may also include wind field sensors for pre-activating the damping system, which may for example bring about a deflection from the neutral position in the damping system, in order thereby to increase a damping path. Such wind field sensors are advantageously arranged on the upwind side.

It is taken as understood that such a pre-activation of the damping system may also be performed using a multiplicity of sensors, for example acceleration, force, rotational speed, rotational angle, position and/or torque sensors, either on their own or in combination.

A multiplicity of actuators may be used with particular advantage within the scope of the present invention. Suitable actuators comprise electrodynamic, piezoelectric, hydraulic (cylinder, membrane) and pneumatic actuators, which may for example also be realized using electroactive polymers, shape-memory actuators or electro- or magneto-rheological fluids.

For example, devices that can be used as adjustable spring elements include those that are disclosed in EP 1 566 543 A1. Hydraulically pretensioned elastomer spring elements for supporting a gear unit on its torque supports are provided here. These elastomer spring elements are connected via hydraulic lines. For damping a torque of a gear unit, a throttling of the fluid exchange of the elastomer spring elements may be performed. In a corresponding way, spring elements such as those known from EP 2 003 362 A2 may be used.

As already explained above, such actuators may be provided at bearing points of torque supports, it being possible for example to use a controlled oil and/or air bubble in the rubber. Apart from single actuators, a number of actuators may be used, in particular connected in series or in parallel, for different frequency ranges, optionally also using different types of these actuators.

In particular for controlling the output power, but also for damping, it may be advantageous for energy to be stored in an accumulator, such as for instance a hydraulic accumulator, a storage battery, a double-layer capacitor, in the form of superconducting coils, flywheels and/or other inertial mass systems. With regard to improved energy efficiency, it is particularly advantageous to use the energy from an actuator for feeding the network, so that an intercepted vibration can also be used for power generation.

Further advantages and refinements of the invention emerge from the description and the appended drawing.

It goes without saying that the features mentioned above and still to be explained below can be used not only in the respectively specified combination but also in other combinations or on their own without departing from the scope of the present invention.

The invention is schematically represented in the drawing on the basis of an exemplary embodiment and is described in detail below with reference to the drawing.

DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic cross-sectional view of a drivetrain of a wind turbine generator system with a device according to a particularly preferred embodiment of the invention.

FIG. 2 shows a schematic longitudinal sectional view of a drivetrain of a wind turbine generator system with a device according to a particularly preferred embodiment of the invention.

FIG. 3 shows a graph illustrating a reduction of vibrations according to a particularly preferred embodiment of the invention.

A transverse sectional view and a longitudinal sectional view of a drivetrain of a wind turbine generator system with a device for reducing loads according to a preferred embodiment of the invention are respectively represented in FIGS. 1 and 2. FIGS. 1 and 2 are explained together, the cross-sectional view being denoted overall by 100 and the longitudinal sectional view being denoted overall by 200.

The drivetrain shown in FIGS. 1 and 2 is substantially made up of a main shaft 10, a gear unit 20 and a generator shaft 30. The gear unit 20 may be, for example, a three-stage gear unit that is conventionally used in wind turbine generator systems. The main shaft 10 is frictionally connected to a rotor, for example a vane rotor R. The gear unit 20 is enclosed by a gear unit housing 21. The generator shaft 30 is connected to a generator 40 via a clutch 31. FIG. 2 additionally shows a main bearing 90, in which the main shaft 10 is mounted.

Torque supports 22 are provided for fixing or supporting the gear unit housing 21. The drivetrain 10 to 30 is mounted as a whole on a machine carrier 60. The mounting itself may be configured for example as elastomer mounting 24, with two bearing bushes 24 a and 24 b respectively for each torque support 22. Damping systems denoted overall by 25 are respectively provided between the machine carrier 60 and the torque supports 22. As explained, the damping systems 25 may have a series of different damping devices, one actuator respectively for each bearing bush 25 a and 25 b being represented by way of example within FIG. 2. The damping devices 25 are adjustable dampers. The control of such dampers is performed on the basis of a control device that is not represented in detail but is schematically indicated in FIGS. 1 and 2 by 70. The control is performed with allowance for a measured-value output of one or more sensors 80 and 82.

The sensors 80 detect a torque fluctuation, for example due to a change in acceleration, in the drivetrain 10 to 30. By means of the sensors 82, an angular offset or a deviation from the ideal alignment of the shafts, is detected, for example laser-optically. The control device 70 controls at least one of the provided damping systems 25 in such a way that an adjusting torque is generated and a torque fluctuation, or torsional flexural torque, is thereby minimized. In a preferred refinement, the adjusting torque is brought about by a rotation or by the raising or lowering of the gear unit 20 or gear unit housing 21.

In order to reduce torsional vibrations, the left-hand torque support 22 is moved upward, for example, by the damping system 25 on the left in FIG. 1 and the right-hand torque support 22 is similarly moved downward by the damping system 25 on the right in FIG. 1. The machine carrier 60 forms the common reference point both for the detection of the torque and for the generation of the adjusting torque, i.e. a variation on the rotational speed in relation to the machine carrier is detected and an active counter-rotation of the gear unit 20 in relation to the machine carrier is brought about. Alternatively, damping may be performed by the damping properties of the damping systems 25 being prescribed variably over time in such a way that a rotation of the gear unit 20 induced by a torque fluctuation is optimally damped.

Dynamic loads that occur when the rotor blades pass the tower during their rotation can be reduced for example by the parallel moving of the damping systems 24 a and/or 24 b shown in FIG. 2. The exact periodic damping sequence, and consequently the moving cycle of the damping means, depends on the number of rotor blades and their rotational speed, and is consequently dependent on the wind turbine generator system that is respectively under consideration.

If it is intended to compensate for flexural torques and forces resulting from a misalignment (a or β), the damping system 25 b on the right in FIG. 2 may, for example, be moved downward or the damping system 25 a on the left in FIG. 2 may be moved upward. The respective opposite damping systems, which in FIG. 2 are concealed, are thereby likewise moved in a corresponding way. Altogether, the compensation for possible alignment errors between the gear unit and the main shaft and/or between the gear unit and the clutch is produced by the raising or lowering of one side or of the complete gear unit 20.

In FIG. 3, a torsional torque 310 without damping and a torsional torque 320 after damping according to a particularly preferred embodiment are represented in the form of a diagram 300, in the form of a torque M on the y axis 302 against a time t of 5 s on the x axis 301. As can be seen, a torsional torque vibration is significantly reduced by the damping behavior according to the preferred embodiment as compared with the undamped state. 

1. A device for reducing loads in the drivetrain of a wind turbine generator system with a machine carrier, comprising: a sensor means configured to detect at least one variable characterizing vibrations and/or misalignments in the drivetrain; an activatable damping means configured to generate at least one adjusting torque, which compensates for at least one torque associated with the load in the drivetrain; and an activating means configured activate the damping means on the basis of the at least one variable detected by the sensor means.
 2. The device as claimed in claim 1, wherein the damping means includes an actuator means, by which an activatable movement of at least one element of the drivetrain in relation to the machine carrier can be brought about.
 3. The device as claimed in claim 1, wherein the damping means includes a braking means, by which an activatable braking of a movement of at least one element of the drivetrain in relation to the machine carrier can be brought about.
 4. The device as claimed in claim 2, wherein the movement is a rotation of the at least one element about an axis of rotation of the drivetrain.
 5. The device as claimed in claim 2, wherein the movement is a raising or lowering of at least one element in relation to the machine carrier.
 6. The device as claimed in claim 1, wherein the sensor means includes speed, acceleration, force, rotational speed, rotational angle, position and/or torque sensors.
 7. The device as claimed in claim 1, wherein the sensor means is configured to detect vibrations and loads with respect to the machine carrier and/or with respect to a surface of the Earth.
 8. The device as claimed in claim 1, wherein the damping means and/or the sensor means is/are provided on torque supports of the drivetrain.
 9. The device as claimed in claim 1, wherein: the device further includes a model and/or an observer means, and the actuating means is configured for a path adaptation.
 10. A method for reducing loads in the drivetrain of a wind turbine generator system, comprising: detecting at least one variable characterizing a vibration and/or a misalignment in the drivetrain; determining at least one torque associated with the load in the drivetrain on the basis of the at least one variable detected; determining at least one adjusting torque; compensating the at least one torque, for reducing the loads; and subjecting at least one element of the drivetrain to the at least one actuating torque determined.
 11. The method as claimed in claim 10, wherein a changing of the torsional and/or flexural torque in the drivetrain is determined on the basis of the variable detected.
 12. The method as claimed in claim 10, wherein the at least one element is rotated and/or raised or lowered in relation to a machine carrier of the wind turbine generator system in an activatable manner and/or the rotational movement of the at least one element is retarded in an activatable manner for subjecting the at least one element of the drivetrain to the at least one actuating torque determined. 